Adsorption mechanism of alkyl hydroxamic acid onto bastnäsite: Fundamental steps toward rational collector design for rare earth elements
Autor: | Santa Jansone-Popova, Alexandra Navrotsky, Vyacheslav S. Bryantsev, Andrew G. Stack, Benjamin Doughty, Anna K. Wanhala, Michael C. Cheshire, Shannon M. Mahurin, Lili Wu |
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Rok vydání: | 2019 |
Předmět: |
chemistry.chemical_classification
Hydroxamic acid Chemistry Metal ions in aqueous solution Inorganic chemistry Infrared spectroscopy chemistry.chemical_element 02 engineering and technology 010402 general chemistry 021001 nanoscience & nanotechnology 01 natural sciences 0104 chemical sciences Surfaces Coatings and Films Electronic Optical and Magnetic Materials Biomaterials Bastnäsite chemistry.chemical_compound Cerium Colloid and Surface Chemistry Adsorption Chemisorption 0210 nano-technology Alkyl |
Zdroj: | Journal of Colloid and Interface Science. 553:210-219 |
ISSN: | 0021-9797 |
Popis: | Rare earth element (REE) production is limited in part by inefficient strategies for beneficiation. Hydroxamic acid ligands are promising reagents for the selective flotation of bastnasite [(Ce,La)FCO3], a major REE ore mineral, but the mechanism and energetics of adsorption are not understood, interfering with the design of new, more efficient reagents. Here, the adsorption of octyl hydroxamic acid onto bastnasite was measured using a combination of experimental and computational methods. In-situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy revealed changes in the hydroxamate functional group vibrational frequencies, corresponding to chelation with cerium cations at the bastnasite surface. The results indicate a monodentate chemisorption mechanism at low surface loading that changes to bidentate chemisorption at higher concentrations. This interpretation is supported by molecular vibrational frequency shifts calculated using density functional theory (DFT), and orientation of the hydrocarbon chain measured by sum frequency generation (SFG) vibrational spectroscopy. The binding enthalpies of octyl hydroxamic acid interacting with La and Ce-bastnasite surfaces were measured using isothermal titration calorimetry (ITC) revealing a stronger coordinating ability with bastnasite than with a common gangue mineral, calcite (CaCO3). Because octyl hydroxamate favors monodentate adsorption at low surface coverages, the relative chelating strength of metal ions could be a poor predictor for selectivity under monolayer adsorption conditions. At higher surface loadings, where the bidentate mode of adsorption is active, selectivity is likely to be limited by increased flotation of gangue ores. |
Databáze: | OpenAIRE |
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